首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   168篇
  免费   12篇
  180篇
  2021年   2篇
  2020年   6篇
  2019年   4篇
  2018年   5篇
  2017年   3篇
  2016年   9篇
  2015年   8篇
  2014年   9篇
  2013年   12篇
  2012年   13篇
  2011年   17篇
  2010年   15篇
  2009年   12篇
  2008年   11篇
  2007年   9篇
  2006年   8篇
  2005年   6篇
  2004年   6篇
  2003年   2篇
  2002年   4篇
  2001年   4篇
  2000年   2篇
  1999年   3篇
  1998年   2篇
  1995年   1篇
  1994年   1篇
  1992年   1篇
  1988年   1篇
  1979年   1篇
  1974年   1篇
  1969年   1篇
  1947年   1篇
排序方式: 共有180条查询结果,搜索用时 15 毫秒
51.
Proliferation of axillary shoots from nodal segments of saucer magnolia (Magnolia x soulangiana Soul.-Bod.) was achieved on modified Standardi and Catalano (S medium) and Lloyd and McCown (WPM) media containing 1.33 μmol·dm−3 BA and 0.54 μmol·dm−3 NAA. The greatest number of axillary shoots was produced on S-medium with full strength macronutrients. Statistically significant were the differences in biomass of axillary shoots cultured in vessels sealed with plastic closures. Rooting of the shoots was achieved on half strength S medium supplemented with 4.9, 9.8, 14.7 and 19.6 μmol·dm−3 IBA. Rooted plantlets were able to resume independent growth after a short period of acclimatization.  相似文献   
52.
Immunosuppressive status in solid organ transplant recipients is often related to the reactivation of Human Cytomegalovirus (HCMV) infection that remains one of the major causes of morbidity and mortality. Therefore, the early detection of HCMV followed by infection monitoring is important to institute prompt and appropriate treatment. In recent years good results have been obtained by HCMV DNA amplification methods; qualitative and quantitative approaches have shown good sensitivity and specificity, but they often require post-PCR manipulation that adds time to the analysis and may lead to contamination problems. Recently, Real Time PCR (RT-PCR) has been proposed in HCMV DNA analysis as a valid method for its good sensitivity and rapidity. In the present study, twenty-five solid organ transplant recipients were analyzed for HCMV diagnosis; 60 peripheral blood leukocytes and 120 plasma samples were tested by RT-PCR and the results compared to those obtained by a qualitative Nested PCR and a quantitative DNA enzyme immunoassay.  相似文献   
53.
Boropinic acid is a natural isopentenyloxycinnamic acid extracted from the aerial parts of Boronia pinnata Sm. (Rutaceae) with soybean 5-lipoxygenase inhibitory activity. In this paper the topical anti-inflammatory activity of boropinic acid and some of its natural and semi-synthetic derivatives was evaluated using the Croton oil ear test in mice as a model of acute inflammation. Some of the tested compounds (15, 17, 19, 20) revealed an effect comparable (ID50 = 0.18 ÷ 0.72 μmol/cm2) to that of the reference drug indomethacin (ID50 = 0.23 μmol/cm2), a non-steroidal anti-inflammatory drug.  相似文献   
54.
The paper deals with the synthesis of organic–inorganic hybrid membranes, Hy, obtained by simultaneous grafting and crosslinking of chitosan with epoxy-terminated polydimethylsiloxane and γ-glycidoxypropyltrimethoxysilane. Porous membranes, HyP, were also obtained by acid decomposition, at different temperatures (25 and 50 °C), of calcium carbonate porogenic agent trapped inside the material. As proved by electron and atomic force microscopy, the non-porous membrane is a phase segregated material with spherical domains (10–40 μm) of silica core covered by hydrophobic siloxane in a hydrophilic chitosan matrix. The porous membranes showed different morphologies with irregular circular pores of 10–30 μm diameters for the membranes obtained at lower temperature, while the membranes prepared at 50 °C tend to adopt a plan-parallel porosity. The water contact angles of hybrid membranes (78°) and pure chitosan membranes (72°) indicated a lower hydrophilic character of modified chitosan. As a result of the crosslinking and of increased hydrophobicity, the hybrid membranes were characterized by a smaller water swelling degree (about 30%) as compared to pure chitosan membrane (700%). However, the presence of the pores in HyP membranes determined an increase of the water adsorption (maximum swelling degree, about 100%). The hybrid membranes possess a slightly higher thermal stability as compared to chitosan (first initial decomposition temperature, 147 and 175 °C for chitosan and hybrid membranes, respectively), but a lower one as compared to pure polydimethylsiloxane. The high storage modulus of chitosan (about 5.1 × 109 Pa at 20 °C) is decreased by about one order of magnitude by the introduction of the highly flexible polysiloxane and the hybrid membranes are more flexible.  相似文献   
55.
Mitochondrial dysfunction has been implicated in rare and common forms of type 2 diabetes (T2DM). Additionally, rare mitochondrial DNA (mtDNA) mutations have been shown to be causal for T2DM pathogenesis. So far, many studies have investigated the possibility that mtDNA variation might affect the risk of T2DM, however, when found, haplogroup association has been rarely replicated, even in related populations, possibly due to an inadequate level of haplogroup resolution. Effects of mtDNA variation on diabetes complications have also been proposed. However, additional studies evaluating the mitochondrial role on both T2DM and related complications are badly needed. To test the hypothesis of a mitochondrial genome effect on diabetes and its complications, we genotyped the mtDNAs of 466 T2DM patients and 438 controls from a regional population of central Italy (Marche). Based on the most updated mtDNA phylogeny, all 904 samples were classified into 57 different mitochondrial sub-haplogroups, thus reaching an unprecedented level of resolution. We then evaluated whether the susceptibility of developing T2DM or its complications differed among the identified haplogroups, considering also the potential effects of phenotypical and clinical variables. MtDNA backgrounds, even when based on a refined haplogroup classification, do not appear to play a role in developing T2DM despite a possible protective effect for the common European haplogroup H1, which harbors the G3010A transition in the MTRNR2 gene. In contrast, our data indicate that different mitochondrial haplogroups are significantly associated with an increased risk of specific diabetes complications: H (the most frequent European haplogroup) with retinopathy, H3 with neuropathy, U3 with nephropathy, and V with renal failure.  相似文献   
56.
57.
Many terrestrial endotherm food webs constitute three trophic level cascades. Others have two trophic level dynamics (food limited herbivores; plants adapted to tackle intense herbivory) or one trophic level dynamic (herbivorous endotherms absent, thus plants compete for the few places where they can survive and grow). According to the Exploitation Ecosystems Hypothesis (EEH), these contrasting dynamics are consequences of differences in primary productivity. The productivity thresholds for changing food web dynamics were assumed to be global constants. We challenged this assumption and found that several model parameters are sensitive to the contrast between persistently warm and seasonally cold climates. In persistently warm environments, three trophic level dynamics can be expected to prevail almost everywhere, save the most extreme deserts. We revised EEH accordingly and tested it by compiling direct evidence of three and two trophic level dynamics and by studying the global distribution of felids. In seasonally cold environments, we found evidence for three trophic level dynamics only in productive ecosystems, while evidence for two trophic level dynamics appeared in ecosystems with low primary productivity. In persistently warm environments, we found evidence for three trophic level dynamics in all types of ecosystems. The distribution of felids corroborated these results. The empirical evidence thus indicates that two trophic level dynamics, as defined by EEH, are restricted to seasonally cold biomes with low primary productivity, such as the artic–alpine tundra and the temperate steppe.  相似文献   
58.

Background

CpG-oligonucleotides (CpG-ODN), which induce signaling through Toll-like receptor 9 (TLR9), are currently under investigation as adjuvants in therapy against infections and cancer. CpG-ODN function as Th-1 adjuvants and are able to activate dendritic cells. In humans TLR9 has been described to be strongly expressed in B-lymphocytes, monocytes, plasmacytoid dendritic cells and at low levels in human respiratory cells. We determined whether a direct interaction of bacterial DNA with the tumor cells themselves is possible and investigated the expression and function of TLR9 in human malignant solid tumors and cell lines. TLR9 expression by malignant tumor cells, would affect treatment approaches using CpG-ODN on the one hand, and, on the other hand, provide additional novel information about the role of tumor cells in tumor-immunology.

Methods

The expression of TLR9 in HOPE-fixed non-small lung cancer, non-malignant tissue and tumor cell lines was assessed using immunohistochemistry, confocal microscopy, in situ hybridization, RT-PCR and DNA-sequencing. Apoptosis and chemokine expression was detected by FACS analysis and the Bio-Plex system.

Results

We found high TLR9 signal intensities in the cytoplasm of tumor cells in the majority of lung cancer specimens as well as in all tested tumor cell lines. In contrast to this non-malignant lung tissues showed only sporadically weak expression. Stimulation of HeLa and A549 cells with CpG-ODN induced secretion of monocyte chemoattractant protein-1 and reduction of spontaneous and tumor necrosis factor-alpha induced apoptosis.

Conclusions

Here we show that TLR9 is expressed in a selection of human lung cancer tissues and various tumor cell lines. The expression of functionally active TLR9 in human malignant tumors might affect treatment approaches using CpG-ODN and shows that malignant cells can be regarded as active players in tumor-immunology.  相似文献   
59.
SNAREs constitute the core machinery of intracellular membrane fusion, but vesicular SNAREs localize to specific compartments via largely unknown mechanisms. Here, we identified an interaction between VAMP7 and SNAP-47 using a proteomics approach. We found that SNAP-47 mainly localized to cytoplasm, the endoplasmic reticulum (ER), and ERGIC and could also shuttle between the cytoplasm and the nucleus. SNAP-47 preferentially interacted with the trans-Golgi network VAMP4 and post-Golgi VAMP7 and -8. SNAP-47 also interacted with ER and Golgi syntaxin 5 and with syntaxin 1 in the absence of Munc18a, when syntaxin 1 is retained in the ER. A C-terminally truncated SNAP-47 was impaired in interaction with VAMPs and affected their subcellular distribution. SNAP-47 silencing further shifted the subcellular localization of VAMP4 from the Golgi apparatus to the ER. WT and mutant SNAP-47 overexpression impaired VAMP7 exocytic activity. We conclude that SNAP-47 plays a role in the proper localization and function of a subset of VAMPs likely via regulation of their transport through the early secretory pathway.  相似文献   
60.
This investigation of microstructure in the human proximal femur probes the relationship between the parameters of the FRAX index of fracture risk and the parameters of bone microstructure. The specificity of fracture sites at the proximal femur raises the question of whether trabecular parameters are site-specific during post-menopause, before occurrence of fragility fracture. The donated proximal femurs of sixteen post-menopausal women in the sixth and seventh decades of life, free of metabolic pathologies and therapeutic interventions that could have altered the bone tissue, constituted the material of the study. We assessed bone mineral density of the proximal femurs by dual energy X-ray absorptiometry and then sectioned the femurs through the center of the femoral head and along the femoral neck axis. For each proximal femur, morphometry of trabeculae was conducted on the plane of the section divided into conventional regions and sub-regions consistent with the previously identified trabecular families that provide regions of relatively homogeneous microstructure. Mean trabecular width and percent bone area were calculated at such sites. Our findings indicate that each of mean trabecular width and percent bone area vary within each proximal femur independently from each other, with dependence on site. Both trabecular parameters show significant differences between pairs of sites. We speculate that a high FRAX index at the hip corresponds to a reduced percent bone area among sites that gives a more homogeneous and less site-specific quality to the proximal femur. This phenomenon may render the local tissue less able to carry out the expected mechanical function.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号